Contractors who reinforced buildings "on the cheap" may have run up the death toll in central Italy's devastating earthquake and could face criminal charges, a local prosecutor said Sunday.

Also Sunday, Pope Francis pledged to visit "as soon as possible" the Italian towns that took the brunt of Wednesday's temblor.

Prosecutor Giuseppe Saieva said the quake that killed at least 290 people may have been more than an unavoidable natural disaster. A quake in the region seven years ago killed more than 300 people and alerted authorities to the need for earthquake-resistant construction. Saieva said property owners who contracted shoddy work could be held responsible for contributing to the damage.

"If the buildings had been constructed as they are in Japan, they wouldn't have collapsed," he told La Repubblica.

Franco Roberti, the head of Italy’s national anti-organized crime agency, told the Italian daily that steps must be taken to ensure that mobsters don't infiltrate reconstruction efforts. Claims of mob involvement in the 2009 reconstruction drew outrage across the nation.

“The risk of infiltration is always high," Roberti said. "Post-earthquake reconstruction is a tasty morsel for criminal organizations and business interests.”

Heavy equipment was digging into rubble Sunday as hopes faded that more survivors would be unearthed amid debris from the magnitude-6.2 quake. Saieva visited a collapsed, three-story villa that he suspected "was built on the cheap with more sand than cement."

Another severely damaged building was an elementary school, empty when the quake hit, that was supposedly rebuilt to be quake-resistant four years ago. Antonio Moretti, a geologist and professor at the University of L'Aquila, said he has visited the site and saw no meaningful adjustments.

"They should have put the iron anchors to the pillars and steel mesh on the walls, but I cannot see that in the rubble," he told La Repubblica.

The national Civil Protection Department had made more than $1 billion available for structural upgrades in earthquake-vulnerable areas.

"If it emerges that individuals cut corners, they will be pursued, and those that have made mistakes will pay a price," Saiva said.

The pope, following Sunday prayers in Rome's St. Peter’s Square, lauded police, volunteer workers and other emergency responders in the region and said their efforts show "how important solidarity is in order to overcome such painful trials."

“Dear brothers and sisters,” he said before leading the throngs in prayer, “I hope to come to see you as soon as possible, to bring you in person the comfort of the faith, the embrace of a father and a brother, and the support of Christian hope.”

Rome is about 90 miles southwest of the ancient town of Amatrice, where the death toll stood at 229 on Sunday. Ten people remained missing in the town of about 3,000 people, and authorities said Sunday they might have located at least three more bodies in the ruins of the Hotel Roma.

"I am certain there is one more person (in the hotel), because it is my uncle," Deputy Mayor Gianluca Carloni told Reuters news service. "It is absolutely vital to finish as soon as possible this initial phase to make sure that there are no more bodies under the rubble."

Another 50 deaths were reported in the town of Arquato del Tronto, with 11 reported in nearby Accumoli.

More than 2,000 people have moved to tent cities, where Mass was held Sunday. Scores of security officials have been sent into the towns to defend against looters.

Italian President Sergio Mattarella visited Amatrice on Saturday, thanking rescue workers who have been grinding non-stop for days. Mattarella and Prime Minister Matteo Renzi also participated in an emotionally charged state funeral in Ascoli Piceno for 35 victims.

“Together we will rebuild our houses and churches, together above all, we will give life back to our communities," Bishop Giovanni D’Ercole told the crowd. "The village bells will ring once more."